1. Field of the Invention
The present invention relates to an ink jet ink, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus.
2. Description of the Related Art
An ink jet recording method is a recording method of applying an ink droplet onto a recording medium such as a plain paper and a glossy medium to form an image on the medium, and becomes increasingly popular because of being inexpensive and having an enhanced recording speed. With the advancement of the high image quality of the image to be obtained by the ink jet recording method and the rapid spread of a digital camera, the ink jet recording method is widely used as a method of outputting an image equivalent to that by a silver salt photography.
In recent years, the image to be obtained by the ink jet recording method has a trend of forming an image of higher quality than before, due to a minimized droplet of ink to be ejected from an ink jet system and a widened color gamut by the introduction of a multicolor ink. However, on the other hand, demands for a coloring material and an ink further increase, and severer characteristics are required for color developability and reliability such as clogging and ejection stability. Particularly, an ink to be applied to the ink jet recording system which ejects an ink from a recording head by an action of a thermal energy and records data is required to have the following characteristics. Specifically, in this case, the ink is required to have such characteristics as not to cause kogation and a break in a heater in the recording head even when the predetermined number of electrical pulses are applied onto the recording head, in other words, as to be superior in recording durability.
On the other hand, an ink jet recording method has a problem that an obtained image may not have sufficient fastness properties (image retainability). Generally, the image obtained by the ink jet recording method shows low image retainability compared to that of the silver salt photograph. Specifically, the image has a problem of easily causing a color tone change and color fading due to the deterioration of a coloring material on the image, when a recording article is exposed to light, moisture, heat, an environmental gas existing in the air and the like for a long period. Particularly, the image which has been recorded by using an ink containing dye as a coloring material has a problem in fastness properties and lightfastness. Among them, the low lightfastness is a problem, which originates in a chemical reaction peculiar to the coloring material.
A large number of technologies are conventionally proposed in order to enhance the lightfastness of the image by solving the problem of the lightfastness. For instance, there is a proposal concerning a black dye having both high fastness properties and color developability (see Japanese Patent Application Laid-Open No. 2005-139427 and International Publication No. WO2006/001274).
There is also a proposal of making bis(2-hydroxyethyl)sulfone contained in an ink to be applied to the ink jet recording method, for the purpose of enhancing the reliability of the ink (see Japanese Patent Application Laid-Open No. H10-060347).